I've always had trouble masking the cowl and ending up with a straight vertical line. I'm working on a P-47 with a red cowl (front). Usually I draw a pencil line freehand and then try to approximate it with about a dozen pieces of tape, since one piece will just curve around on the opposite side and not produce a straight line.

A tip I have used to mark vertical pnel lines on RC aircraft, is to to mount the plane on its nose and attaching pencil to a block and revolving the block round the plane. Hey presto perfectly straight parrallel vertical lines.

As sor the masking part. Use one strip of 2mm wide tape to follow line then wider tape to complete mask if spraying. Hope this makes sense.

Yes, makes perfect sense. I will try it. The thin tape is the way to go with establishing that straight line, then I can use wider tape on the other side of it. I think I've been doing it the hard way.

Northwest,
Funny you're doing a P-47. The one and only time I needed to mask off a cowling was a white-nosed T-bolt.
What I did was paint the whole cowling white, wait for it to dry a day or so, then put a big fat snug rubber band around the white. I adjusted the band until it was straight all the way around. Added some masking around the nose where the band didn't cover the white area. Shot the topside and underbelly colors, removed the band and I had a perfect white nose.
Since rubber bands come in so many sizes and thicknesses, it was just a matter of sifting through a variety pack of them until I found one that fit snugly.
Really worked a lot better than I expected.

I go with the thin tape idea; I use painter's masking tape usually, and cut a strip about 1mm wide, and use that to go round the curved areas. Then fill in the holes, as explained above. What I really hate is these curved coloured areas you find on late-war USAAF fighters, both P-47s and P-51s! Good job I rarely do USAAF aircraft...

The P-47D I'm doing is a tricky one. It is Gabresky's plane from late 1944. I think I've got as much info as is available about the camo paint. But, what I found interesting is that the two decal kits I had both had the Pilot/Crew plackard wrong. The AeroMaster and the Techmod decals had either the wrong ranks or wrong people.

I believe that at the time of his last victory before crashing, his rank was LT COL and his crew was: Crew Chief S/SGT Ralph H. Safford, Asst. SGT Felix Schacki, Armorer S/SGT John Koval, Asst. SGT Giuseppe (Joe) DiFranzia.

So, that is what I put on the little tiny decal I made with my new Testor's decal kit. Worked great, but after quite a lot of fussing.